questions and tells us why we should believe he's a changed man. >> announcer: from the global resources of abc news, with terry moran, cynthia mcfadden and bill weir in new york city, this is "nightline," july 18th, 2012. >> good evening, i'm cynthia mcfadden. tonight, the frantic hunt for clues in the mysterious disappearance of two young girls in a tiny iowa town. six days ago, they went out on a bike ride but never returned. triggering a sweeping fbi search, with the help of hundreds of local volunteers. but still, no substantial leads, on a trail growing colder by the minute. abc's alex perez comes to us from evansdale, iowa. >> reporter: it's the mystery that's turning the tiny town of evansdale, iowa, upside down. >> the more time and things that go by, you know, more thoughts that go through your head and the worse the pit in your stomach gets. >> elizabeth collins and lyric cook vanishes after leading for a bike ride friday, seemingly without a trace. the only clue, their two bicycles, found at the edge of this local lake. that was five days ago. so far, no break in the case. ho